// CHECKSTYLE_OFF: Copyrighted to the Android Open Source Project.
/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
// CHECKSTYLE_ON

package java.io;

/**
 * Wraps an existing {@link InputStream} and performs some transformation on the input data while it
 * is being read. Transformations can be anything from a simple byte-wise filtering input data to an
 * on-the-fly compression or decompression of the underlying stream. Input streams that wrap another
 * input stream and provide some additional functionality on top of it usually inherit from this
 * class.
 *
 * @see FilterOutputStream
 */
public class FilterInputStream extends InputStream {

  /** The source input stream that is filtered. */
  protected volatile InputStream in;

  /**
   * Constructs a new {@code FilterInputStream} with the specified input stream as source.
   *
   * <p><strong>Warning:</strong> passing a null source creates an invalid {@code
   * FilterInputStream}, that fails on every method that is not overridden. Subclasses should check
   * for null in their constructors.
   *
   * @param in the input stream to filter reads on.
   */
  protected FilterInputStream(InputStream in) {
    this.in = in;
  }

  @Override
  public int available() throws IOException {
    return in.available();
  }

  /**
   * Closes this stream. This implementation closes the filtered stream.
   *
   * @throws IOException if an error occurs while closing this stream.
   */
  @Override
  public void close() throws IOException {
    in.close();
  }

  /**
   * Sets a mark position in this stream. The parameter {@code readlimit} indicates how many bytes
   * can be read before the mark is invalidated. Sending {@code reset()} will reposition this stream
   * back to the marked position, provided that {@code readlimit} has not been surpassed.
   *
   * <p>This implementation sets a mark in the filtered stream.
   *
   * @param readlimit the number of bytes that can be read from this stream before the mark is
   *     invalidated.
   * @see #markSupported()
   * @see #reset()
   */
  @Override
  public void mark(int readlimit) {
    in.mark(readlimit);
  }

  /**
   * Indicates whether this stream supports {@code mark()} and {@code reset()}. This implementation
   * returns whether or not the filtered stream supports marking.
   *
   * @return {@code true} if {@code mark()} and {@code reset()} are supported, {@code false}
   *     otherwise.
   * @see #mark(int)
   * @see #reset()
   * @see #skip(long)
   */
  @Override
  public boolean markSupported() {
    return in.markSupported();
  }

  /**
   * Reads a single byte from the filtered stream and returns it as an integer in the range from 0
   * to 255. Returns -1 if the end of this stream has been reached.
   *
   * @return the byte read or -1 if the end of the filtered stream has been reached.
   * @throws IOException if the stream is closed or another IOException occurs.
   */
  @Override
  public int read() throws IOException {
    return in.read();
  }

  @Override
  public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {
    return in.read(buffer, byteOffset, byteCount);
  }

  /**
   * Resets this stream to the last marked location. This implementation resets the target stream.
   *
   * @throws IOException if this stream is already closed, no mark has been set or the mark is no
   *     longer valid because more than {@code readlimit} bytes have been read since setting the
   *     mark.
   * @see #mark(int)
   * @see #markSupported()
   */
  @Override
  public void reset() throws IOException {
    in.reset();
  }

  /**
   * Skips {@code byteCount} bytes in this stream. Subsequent calls to {@code read} will not return
   * these bytes unless {@code reset} is used. This implementation skips {@code byteCount} bytes in
   * the filtered stream.
   *
   * @return the number of bytes actually skipped.
   * @throws IOException if this stream is closed or another IOException occurs.
   * @see #mark(int)
   * @see #reset()
   */
  @Override
  public long skip(long byteCount) throws IOException {
    return in.skip(byteCount);
  }
}
